Whats the cheapest way of filling a hole on the outside of a wall?

Basically we have a brick on the outide of our house with four round holes in it obviously used to be a vent of some kind. the kitchen has been moved around so much that this vent is behind my washing machine the holes come straight through to the kithen (cold!) basically i want to fill them as cheaply as poss what do i use cocrete? polyfila? i am not that great when it comes to diy but its freezin my house out! i cannot board it over either the bricks for the house are forigen furnace bricks and are imposible to get a nail through.
Answer
Can of filler foam, fill holes with it, i did 3 year ago and it is still holding up.